Major metropolitan areas of the United States, and some foreign countries, have an emergency telephone system that allows a caller having a need for emergency, e.g., medical or police, assistance to be connected to a location that can provide the assistance, commonly called a public service answering point (PSAP). In the U.S., a universal number--9-1-1--is used to access the emergency telephone system in areas where it is available. As a result, such systems have come to be known as 9-1-1 systems, as well as emergency telephone systems.
In the past, 9-1-1 systems have used dedicated lines to connect the local office receiving a 9-1-1 call to a PSAP. In areas of high population density, i.e., major metropolitan areas, the cost of dedicated lines is justified by the relatively short line runs and the relatively large use of 9-1-1 service on a per capita basis.
In recent years, attempts have been made to extend 9-1-1 service to rural communities and to communities located near, but outside of, major metropolitan areas. In the past, in order to maintain the reliability of 9-1-1 service, rural 9-1-1 systems, like metropolitan 9-1-1 systems, have used dedicated lines to couple rural central offices to a PSAP, which may be located in a central rural community or a nearby metropolitan area. While more reliable, dedicated lines are very expensive when compared with the shared trunks utilized by the public telephone network (PTN). More specifically, as well known to those familiar with telephone communication networks, the public telephone network comprises central offices that include switches that control telephone communication via trunks that connect the central offices together. Sharing of trunks reduces telephone call costs. Unfortunately, shared trunks are not as reliable as dedicated lines. Calls can be misdirected through central office switches and central office switches can break down, for example. On the other hand, dedicated lines are expensive, particularly when they are idle most of the time. In some cases, the high cost of dedicated lines has prohibited the implementation of 9-1-1 service, particularly in rural areas.
The present invention is directed to providing a public telephone network emergency telephone system having the same or greater reliability as does a dedicated line emergency telephone system.